1. Field of the Invention
The subject disclosure relates to unitized bearing seal assemblies, and more particularly to, a low torque seal assembly wherein open cell filter media is utilized to partially define a circuitous sealing labyrinth and to maintain lubricant within an interior bearing chamber and exclude contaminants therefrom.
2. Background of the Related Art
Ball and roller bearing assemblies are well known in the art and have been used for many years in applications such as railway cars, crane wheels and trucking. Bearing assemblies are typically provided as a self-contained unit and generally include a plurality of circumferentially-spaced balls or rollers confined between concentric outer and inner rings or cylinders. The concentric rings define an interior chamber for containing the rolling elements and supply smooth, hard, accurate surfaces for the balls or rollers to roll on. These surfaces are referred to as races or raceways. A uniform spacing is maintained between adjacent balls or rollers within the interior chamber by a cage or separator element and a lubricant such as grease is applied therein. The rolling elements are the most important component of the bearing assembly, because they transmit the loads from the moving parts of the machine to the stationary support. The balls are ideally uniformly spherical, but the rollers may be straight cylinders, or they may be tapered, cone-shaped or other forms depending upon the purpose of the design. Additionally, the balls or rollers can be provided in a single row or multiple rows.
Bearing assemblies are typically dimensioned and configured such that they can be installed by sliding the assembly over an axle journal and into a housing. The inner ring is typically engaged with the axle journal and the outer ring is engaged with the housing so as to enable the axle to rotate relative to the housing or vise versa. Bearing assemblies often operate in hostile environments, and this is particularly true when they are used in application such as railcars. As a result, the interior chamber which contains the rolling elements, must be sealed so that contaminants, such as dirt and water, are kept out and lubricant is kept in.
U.S. Pat. No. 4,770,548 to Otto discloses a hydrodynamic seal which is suitable for closing the end of a tapered roller bearing assembly. The seal includes a seal case which is pressed into a counterbore formed in the end of the outer ring (cup) and an elastomeric sealing element. The elastomeric sealing element has a primary lip and a secondary lip which cooperate with a sealing surface on a thrust rib on the inner ring (cone) to effect a live seal along the surface. The secondary lip is in direct contact with the sealing surface of the thrust rib with the primary lip being slightly offset therefrom.
U.S. Pat. No. 4,819,949 also to Otto discloses a seal assembly for closing the end of a tapered roller bearing. The seal assembly is a unitized assembly which includes interlocked seal and shield portions. The seal portion is a two-piece unit which consists of a rigid case and a flexible sealing element. The rigid case is mounted to the outer ring of the bearing and the flexible sealing element is bonded to the outboard end of the rigid case. The flexible sealing element has a dirt lip directed obliquely toward and contacting the shield portion, and a secondary lip also directed obliquely toward the shield portion, but it is not in contact with the shield portion.
Radial lip seals which contact the sealing surface, like those disclosed in the Otto patents, are common. Although contacting lip seals adequately perform the sealing function, the contact between the lip and the sealing surface causes seal wear and a loss of power in the rotating system due to friction between the two surfaces. In addition to the interference between the lip and the sealing surface, the elasticity of the rubber element and the spring force (if used) applied thereto creates a radial load which results in additional torque requirements and the generation of heat. Still further, while these lip seals adequately perform the sealing function, they do not provide a mechanism for exhausting the bearing chamber. More specifically, during operation of the bearing seal assembly, positive contacting lip seals do not provide for ventilation of the bearing chamber and therefore, the temperature within the bearing chamber increases and pressurized gases are created. Both of these conditions adversely impact the performance and wear of the bearing seal assembly.
There is a need therefore, for a seal assembly which excludes contaminants, such as water and dirt, from within the interior bearing chamber and retains the lubricant therein, while requiring less torque to rotate than a conventional radial lip seal and providing a mechanism for bidirectional movement of gases between the bearing chamber and seal exterior to equalize the pressure.
The subject disclosure relates to a labyrinth seal assembly for sealing an annular gap defined between a bore of a housing and an outer surface of a cylindrical shaft, wherein the housing and shaft are relatively movable. The seal assembly includes radially inner and radially outer shield rings. The radially inner shield ring has an inner surface which is adapted and configured for support by the shaft. The inner shield ring defines a sealing channel which includes at least one sealing surface.
The radially outer shield ring is partially disposed within the sealing channel of the inner shield ring. The outer shield ring includes a casing member, at least one foam seal element, and a shield element retainer. The casing member includes opposed first and second axially extending portions, the first axially extending portion adapted and configured for engagement with the housing. In a preferred configuration, the first axially extending portion is positioned axially offset from and radially outward of the second axially extending portion and the casing member further includes a radially extending shoulder portion which connects the first axially extending portion to the second axially extending portion.
The seal element retainer is engaged with the second axially extending portion of the casing member and the at least one foam seal element depends radially inward therefrom into the sealing channel so as to form a circuitous sealing labyrinth therein.
It is envisioned that the seal assembly further includes a highly viscous fluid disposed within the circuitous sealing labyrinth. In one embodiment, the highly viscous fluid is a water insoluble grease. Alternatively, the highly viscous fluid can be a ferrofluid. In this embodiment it is preferred that the at least one foam seal element include a conventional magnet.
Preferably, the at least one foam seal element is formed from polyurethane and includes first and second foam seals. It is presently envisioned that the first foam seal has a material density which is greater than a material density for the second foam seal. More specifically, the first foam seal element has a pore size of 20 pores per inch and the second foam seal has a pore size of 45 pores per inch.
The seal element retainer is engaged with the second axially extending portion by means of a press fit. Those skilled in the art will readily appreciated that alternative mechanisms for engaging the seal element retainer with the second axially extending portion of the casing member can be used without departing from the inventive aspects of the present disclosure. In a preferred embodiment, seal element retainer includes a first baffle ring which has an arm portion that depends radially inward into the sealing channel. It is presently envisioned that the seal element retainer is formed from a plastic material and the at least one foam sealing element is adhered thereto.
The seal assembly of the present disclosure can further include a second baffle ring which has a shoulder portion and an arm portion. The shoulder portion is engaged with the inner shield ring and the arm portion depends from the shoulder portion so as to extend radially outward into the sealing channel.
The present disclosure is also directed to a bearing assembly for placement between a bore of a housing and an outer surface of an elongated axle. The bearing assembly includes an outer cylinder, an inner cylinder, a plurality of bearings, and at least one labyrinth seal assembly.
The outer cylinder has axially opposed first and second ends and defines a first race surface on an inner diameter thereof and a central axis for the bearing assembly. The inner cylinder is coaxially positioned within the outer cylinder and defines a second race surface on an outer diameter thereof, wherein a bearing chamber is defined between the outer cylinder and the inner cylinder. The plurality of bearings are disposed within the bearing chamber and are in rolling contact with the first and the second race surfaces. Each bearing facilitates the relative rotational movement between the inner cylinder and the outer cylinder.
The labyrinth seal assembly is associated with the first end of the outer cylinder and seals the bearing chamber defined between the outer cylinder and the inner cylinder. The seal assembly includes radially inner and radially outer shield rings. The radially inner shield ring has an inner surface which is adapted and configured for support by the shaft. The inner shield ring defines a sealing channel which includes at least one sealing surface.
The radially outer shield ring is partially disposed within the sealing channel of the inner shield ring. The outer shield ring includes a casing member, at least one foam seal element, and a shield element retainer. The casing member includes opposed first and second axially extending portions, the first axially extending portion adapted and configured for engagement with the housing.
As before, it is envisioned that the seal assembly further includes a highly viscous fluid disposed within the circuitous sealing labyrinth. In one embodiment, the highly viscous fluid is a water insoluble grease. Alternatively, the highly viscous fluid can be a ferrofluid. In this embodiment it is preferred that the at least one foam seal element includes a conventional magnet or electromagnet.
The present disclosure is also directed to a labyrinth seal assembly for sealing an annular gap defined between a bore of a housing and an outer surface of an elongated axle, wherein relative rotational movement exists between the axle and the housing. The seal assembly includes radially inner and outer shield rings. The radially inner shield ring has an inner surface adapted and configured for support by the axle. The inner shield ring defines a sealing channel which includes at least one sealing surface.
The radially outer shield ring includes a casing member, a first baffle ring, and first and second foam seal elements. The casing member has axially opposed first and second end portions. The first end portion is adapted and configured for engagement with the bore of the housing and the second end portion is partially disposed within the sealing channel so as to form a first section of a circuitous sealing labyrinth. In a representative embodiment the first axially extending portion is positioned axially offset and radially outward of the second axially extending portion and the casing member further includes a radially extending shoulder portion which connects the first axially extending portion to the second axially extending portion.
The first baffle ring has a shoulder portion and an arm portion. The shoulder portion is engaged with the second end portion of the casing member. The arm portion depends radially inward from the shoulder portion into the sealing channel.
The first and second foam seal elements are disposed within the sealing channel so as to form a second portion of the circuitous sealing labyrinth. The first foam seal element is engaged with the first baffle ring and the second foam seal element is affixed to the second end portion of the casing member.
Preferably, the first foam seal has a material density which is greater than a material density for the second foam seal. In a representative embodiment, the first foam seal element has a pore size of 20 pores per inch and the second foam seal has a pore size of 45 pores per inch. It is envisioned that the foam seal elements are formed from polyurethane.
The first baffle ring is engaged with the second axially extending portion by means of a press fit. Alternative mechanisms of engaging the baffle ring with the second axially extending portion of the casing member can be used without departing from the inventive features and methods disclosed herein. Preferably, the first baffle ring is formed from a plastic material.
In a alternate embodiment, the seal assembly further includes a second baffle ring which has a shoulder portion and an arm portion. The shoulder portion is engaged with the inner shield ring and the arm portion depends from the shoulder portion so as to extend radially outward into the sealing channel.
Those skilled in the art will readily appreciate that the seal assembly of the subject disclosure excludes contaminants from within the bearing chamber and prevents lubricant from escaping therefrom while requiring less torque to rotate, thereby reducing power losses in the rotating system. Additionally, the open celled foam elements allow air to migrate between the bearings and the environment, while blocking contaminants such as dirt and water. These and other unique features of the unitized seal assembly disclosed herein will become more readily apparent from the following description, the accompanying drawings and the appended claims.